T CELL RECEPTOR MEDIATED SIGNALING Multisubunit Immune Recognition Receptors MIRR α β ε δ ε γ ζ ζ ITAM Immunoreceptor Tyrosine-based Activation Motif ACTIVATION

THE ADHESION AND CO-STIMULATORY MOLECULES CD4 AND CD8 MARKERS OF T CELL SUBPOPULATIONS ADHESION MOLECULE BINDS TO MHC SIGNALING MOLECULE TARGET CELL 1 3 2 2m 2 1 2 1 PROFESSIONAL APC CD8 Cytotoxic T-cell α β Helper T-cell CD4 SIGNAL

THE RATIO OF CD4+/CD8+ T CELLS IS STABLE IN HEALTHY INDIVIDUALS Normal CD4+ T-cell counts = 600 – 1400/ l HIV infection  AIDS = CD4+ T cell count <200/l

Jelátviteli utak T-sejtekben Fyn

Transzkripciós faktorok szerepe a T-sejt aktivációban

Antigen presentation - T cells are co-stimulated APC Th Signal 1 antigen & antigen receptor ACTIVATION Signal 2 B7 family members (CD80 & CD86) CD28 Costimulatory molecules are expressed by professional APC including dendritic cells, monocytes, macrophages, and B cells, but not by cells that have no immunoregulatory functions such as muscle, nerves, hepatocytes, epithelial cells etc.

ROLE OF CO-STIMULATION IN THE ACTIVATION OF HELPER T CELLS B7 CD28 CD40 CD40L B7 APC APC APC NORMAL TISSUE CELLS DO NOT EXPRESS CD40 OR B7 CO-STIMULATORY MOLECULES

T CELLS REQUIRE TWO SIGNALS TO GET ACTIVATED APC not presenting antigen Activated APC Resting APC B7 B7 CD4 CD4 CD4 CD28 CD28 CD28 2 1 1 2 T-cell activation T-cell anergy No effect ANTIGEN SPECIFIC ACTIVATION, ANERGY OR NEGLECTION

Mechanism of co-stimulation in T cells 1 Antigen IL-2 IL-2R IL-2 IL-2R Resting T cells Signal 1 NFAT binds to the promoter of of the a chain gene of the IL-2 receptor. The a chain converts the IL-2R to a high affinity form Express a low affinity IL-2 receptor-  and  chains and produce no IL-2

Mechanism of co-stimulation in T cells 2 Costimulation 1 Antigen Signal 2 Activates AP-1 and NFk-B to increase IL-2 gene transcription by 3 fold Stabilises and thus increases the half-life of IL-2 mRNA by 20-30 fold IL-2 production increased by 100 fold overall IL-2 IL-2R Immunosuppressive drugs illustrate the importance of IL-2 in immune responses Cyclosporin & FK506 inhibit IL-2 by disrupting TcR signalling Rapamycin inhibits IL-2R signalling

Signal Transducer and Activatior of Transcription THE HIGH AFFINITY IL-2 RECEPTOR IL-2 CYTOSKELETON β γ α Ligand binding No signaling JAK Janus kinase STAT Signal Transducer and Activatior of Transcription Gene transcription Proliferation

THE IL-2 RECEPTOR FAMILY – hematopoiesis Affinity low medium high medium no signal no signal signal signal α β γ α β γ IL-2R IL-15RI IL-7R IL-9R IL-4RI Loss of function mutation of the -chain results in X-linked inherited severe combined immunodeficiency (X-SCID syndrome)

AUTOCRINE GROWTH FACTOR adhesion costimulation recognition INITIATION OF T CELL PROLIFERATION IL-2R IL-2 IL-2Rα IL-1 IL-2R low affinity high affinity IL-2 transferrin insulin IL-2 AUTOCRINE GROWTH FACTOR PROLIFERATION

1 Anergy Antigen Naïve T cell Signal 1 only IL-2 IL-2R 1 Antigen Signal 1 only Epithelial cell The T cell is unable to produce IL-2 and therefore is unable to proliferate or be clonally selected. Unlike immunosupressive drugs that inhibit ALL specificities of T cell, Signal 1 in the absence of signal 2 causes T cell unresponsiveness to a specific antigen Self peptide epitopes presented by a non-classical APC e.g. an epithelial cell

CO-STIMULATION IS ESSENTIAL FOR PRIMING OF NAIVE T LYMPHOCYTES The antigen-specific and the co-stimulatory signals have to be induced in concert to induce T lymphocyte activation The antigen-specific and co-stimulatory signals can be delivered simultaneously by professional antigen presenting cells, only The antigen-specific and the co-stimulatory singnals has to be delivered by the same professional antigen presenting cell

Coreceptors deliver powerful responses Dangers of triggering strong co-stimulatory signals Mice are not humans

Cytokine storm in a phase 1 trial of the anti-CD28 monoclonal antibody TGN1412. Suntharalingam G, Panoskaltsis N. N Engl J Med. 2006 Sep 7;355(10):1018-28. Six healthy young male volunteers at a contract research organization were enrolled in the first phase 1 clinical trial of TGN1412, a novel superagonist anti-CD28 monoclonal antibody that directly stimulates T cells. Within 90 minutes after receiving a single intravenous dose of the drug, all six volunteers had a systemic inflammatory response characterized by a rapid induction of proinflammatory cytokines and accompanied by headache, myalgias, nausea, diarrhea, erythema, vasodilatation, and hypotension. Within 12 to 16 hours after infusion, they became critically ill, with pulmonary infiltrates and lung injury, renal failure, and disseminated intravascular coagulation. Severe and unexpected depletion of lymphocytes and monocytes occurred within 24 hours after infusion. All six patients were transferred to the care of the authors at an intensive care unit at a public hospital, where they received intensive cardiopulmonary support (including dialysis), high-dose methylprednisolone, and an anti-interleukin-2 receptor antagonist antibody. Prolonged cardiovascular shock and acute respiratory distress syndrome developed in two patients, who required intensive organ support for 8 and 16 days. Despite evidence of the multiple cytokine-release syndrome, all six patients survived. Documentation of the clinical course occurring over the 30 days after infusion offers insight into the systemic inflammatory response syndrome in the absence of contaminating pathogens, endotoxin, or underlying disease.

Modulation of the CD28 co-stimulatory pathway. „Extreme response The drug, an antibody called TGN1412, is being developed by German company TeGenero with the aim of directing the immune system to fight cancer cells, or calm joints inflamed by rheumatoid arthritis. The antibody binds to a receptor molecule called CD28 on the surface of the immune system's infection-fighting T cells. (Nature March 17 2006) Scientists who work in the field say there are several possible ways that the drug could have triggered multiple organ failure. It may have stimulated T cells so much that they released an overwhelming flood of inflammatory molecules called cytokines. Or perhaps wayward T cells launched an attack on the body's own tissues, ignoring the safety mechanisms that normally keep this in check.

MECHANISM OF THE ACTION OF THE IMMUNE SUPPRESSIVE DRUG CYCLOSPORIN A AND FK506/PROGRAPH TCR-CD3 Other receptors Inactive phosphatase Aktive phosphatase FK506 CSA Dephosphorylation of cytoplasmic NF-AT induces translocation to the nucleus FKBP2 isomerase Cycliphilin A isomerase Cytokines, activation molecules IL-2, IL-2R TGF NOT ANTIGEN SPECIFIC